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Junction Style Guide/Interchange

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Name inheritance, but signage on consecutive signs are different
Extend the ramp naturally to create a junction with the road segment at a 20° departure angle. This will allow for consistent timing of exit instructions and make it easier to report closures in the Waze client.
Likewise, at At the end of an entrance ramp place a geometry node at the end of the solid white line and extend the ramp to join with the highway at a 20° reasonable departure anglethat follows the natural road geometry. This will The angle used should allow for smooth and consistent auto-zoom functionality—the client remains zoomed in for the duration of the ramp, zooming out when the user gets on the freeway.
Rule #1 is still simpler is better. If there is no large distance between paths at the end of a ramp (either into or out of the ramp), a single segment connecting to a single junction node is all that is needed. The existence of a painted, concrete, or grass island is '''not''' enough of a reason to divide a ramp into multiple ramps.
: [[ImageFile:Jct_ramp_no_splitJunction_style_simple_ramp_(2).pngPNG|400px]]
When paths at the end of the ramp deviate significantly in distance, regardless of the existence of any type of island, then multiple ramps should be used.
: [[ImageFile:Jct_ramp_splitJunction Style ramp split.pngPNG|350px]]
== {{anchor|Interchange types}}Component junction types ==
Specific examples of how to handle common junction types are provided in the following sections. All of those examples use these road types. If you are unsure what road type you should use, refer to the [[road types]] article.
=== {{anchor|Exits}}Basic exit/entrance ===
A basic exit is a junction where a single ramp exits a highway and leads to another road, and the continuation of the highway is obvious to drivers. Most exits fit this description.
Similarly, a basic entrance is where a single ramp joins an existing highway, and the path of the highway is obvious to drivers. The geometry of a basic entrance junction should be mapped just like a basic exit, but with directions reversed.
==== {{anchor|Exit geometry}}Basic exit geometry ====
: [[Image:Jct_fwy_exit.png]] [[Image:Jct_maj_exit.png]] [[Image:Jct_min_exit.png]]
See [[#Ramp geometry and complexity|ramp geometry and complexity]] for information on setting the angles of basic exits.
==== {{anchor|Exit naming}}Basic exit naming ====
The highway/freeway segments before and after the junction should be named the same. The ramp segments should be named in accordance with the section on [[Road names#Exit|exit ramp names]]. In addition, if an exit carries a concurrent route away from the highway, for example a US route that was carried by an interstate up to the exit but splits off at the exit, that route designation should be added as an alternate name on all ramp segments that carry it.
=== {{Anchor|Wayfinders|Terminology|Criteria|Configuration|Segment naming}}Complex exit ===
A complex exit is a junction where one or more exit ramps leave the highway, and the continuation of the highway is not obvious to drivers. Therefore, another instruction is needed for traffic continuing on the highway. This can be a "keep" or "continue" instruction. When mapping complex exits, the geometry should match the instruction given, so for "continue" instructions the geometry should be set up as described for exits in [[#Ramp geometry and complexity|ramp geometry and complexity]], and for keep instructions (i.e. most wayfinder exits), the geometry should be set up in the same way as a [[#Freeway fork geometry|freeway fork]]. For criteria and further details on mapping complex exits, see [[wayfinder]] and [[turn instruction override]].
=== {{anchor|Freeway/highway splits|Freeway/highway forks}} Freeway/highway fork===
A highway/freeway fork is a junction where one freeway or highway splits into two, and there is no obvious straight through direction for a driver. This can happen at the end of a concurrency of highway routes or where one or both highway routes begin. This is synonymous with the MUTCD term "split."
For further details on freeway fork mapping, see the [[wayfinder]] page.
=== {{anchor|Ramp-ramp forks}}Ramp fork ===
A ramp may itself fork and branch into two directions. This is synonymous with the MUTCD term "bifurcation." Most of the time a ramp fork should be mapped to give instructions to traffic going either direction. This is accomplished by using the ramp type for both outgoing segments and names that are different from the incoming segment or turn instruction overrides where necessary.
Naming of ramp forks should generally follow the guidelines from [[Road names#Exit|road names]], but there are multiple ways to handle all the signs present at each junction.
===== Using information on the signs directly =====A simple way to name the ramp segments in ramp forks is to name each ramp segment with full or abbreviated information shown on the signs leading into it. This will provide a static set of instructions for users as they travel on each segment, regardless of what their further movements will be. This is especially appropriate when a single sign is present at an exit, but multiple signs with different information are present farther down the road. ===== Using road name inheritance =====[[File:RampforkMUTCD.png|thumb]]
Another way to name these ramp segments is to use name inheritance. If a ramp is unnamed ("no name" box checked), the name of a subsequent ramp on the route will propagate backwards in navigation instructions. This is useful both for the sake of simplicity and for giving more specific instructions to traffic at exits with ramp forks. If an unnamed ramp is used at an exit and subsequent named ramps are used after the fork, drivers will only see the name of whichever side of the fork they need to go to before they exit the highway. This method will provide more sufficient notification of an approaching decision point than a named exit ramp would, and it should be used as long as the names of both ramp forks are visible on signs at the start of the initial ramp. If an exit ramp has multiple lanes with a sign or part of a sign over each lane, using this method can even function as a form of lane guidance. If the example on the right from the MUTCD were mapped using name inheritance, the ramp exiting I-42 would not be named. The ramp that goes to I-17 southbound would be named "Exit 36: I-17 S / Portland" and the ramp that goes to I-17 northbound would be named "Exit 36: I-17 N / Miami." This would produce the following instructions:
*# at the exit: exit right to Exit 36: I-17 N / Miami
*# at the fork: keep left to Exit 36: I-17 N / Miami
Note that even though the exit number is by design not shown on signs at the ramp fork, it should be included in the names of the ramps for proper instructions at the exit. If signs at the ramp fork differ more significantly from signs at the exit, a different method of naming should be used. ====== Name inheritance, but signage on consecutive signs are different ======[[File:PseudoWF.png|thumb]]
If separate or split signs exist for traffic at an exit, but the signs at the ramp fork differ significantly from them, such as being further split or showing additional route numbers or control cities, the following method can be used:
* # Leave the exit ramp unnamed* # At the ramp fork create a turn instruction override for no instruction going into a stub ramp segment of {{:Segment length/Minimum}}* # Name the stub according to the sign at the ''exit''* # At the junction of the stub with the next ramp segment create a turn instruction override to match the expected instruction at the ramp fork, either keep left or right* # Name the next ramp segment according to the sign at the ''ramp fork'' or leave it unnamed to inherit farther ramp names
Because of name inheritance, the shortness of the stub, and the combination of turn instruction overrides, the name of the stub will be used in instructions at the exit, and the name of the ramp past the stub will be used at the ramp fork. This method should only be used when it's not possible to replicate what drivers see on guide signs using simple naming or name inheritance.
== {{Anchor|Interchange configurations}}Configurations ==
=== {{anchor|Diamond interchange}}Diamond ===: [[ImageFile:Jct_diamondDiamond interchange.pngPNG|750px]]
''See also: [[Wikipedia:Diamond_interchange|Diamond interchange article on Wikipedia]]''
The straight through motion from the exit ramp to the entrance ramp should typically be enabled, if legal to drive. Under normal circumstances, the big detour prevention mechanism discourages the routing server from routing someone off the freeway and directly back on. When the freeway path between the ramps is closed, or slow enough to overcome the Detour penalty, this off-on route may be given as a desirable alternative.
Be aware that the big detour prevention penalty is intended to discourage routing that leaves a freeway (or highway) and returns to the same freeway (or highway). Therefore, at least one name (primary or alternate) of the freeway/highway segment before the exit ramp must exactly match one name (primary or alternate) of the freeway/highway segment after the entrance ramp to trigger the penalty. For further information see the b[[Detour Prevention Mechanisms|ig big detour prevention mechanism]] page.
If the ramps connect to the surface street at multiple points, restrict turns which should use another ramp. Review the section on [[Junction Style Guide/InterchangesInterchange#Ramp geometry and complexity|ramp geometry and complexity]] for more details on this topic.
First we see the turns that must be restricted for the exit ramps:
The single surface street segment between the inner most ramps should be either raised or lowered in relation to the freeway segments depending on the actual geography at the interchange.
=== {{anchor|Cloverleaf interchange}}Cloverleaf ===
: [[Image:Jct_cloverleaf.png]]
'''Note on elevation: '''The single surface street segment between the inner most ramps should be either raised or lowered in relation to the freeway segments depending on the actual geography at the interchange.
=== {{anchor|Folded diamond interchange}}Folded diamond ===
: [[Image:Jct_folded_diamond.png]]
''See also: Discussion of Folded Diamonds and A2/B2 Partial Cloverleafs on the [[wikipedia:Partial_cloverleaf_interchange|Partial Cloverleaf Interchange article on Wikipedia]]''
=== Single-point urban interchange (SPUI) ===
: [[ImageFile:Jct_SPUISPUI.pngPNG|750px]]
''See also: [[wikipedia:Single-point_urban_interchange|Single Point Urban Interchange article on Wikipedia]]''
The outer branches of the exit ramps are similar to a diamond interchange and ramp to ramp routing should be enabled if possible and legal. However, in many SPUIs such ramp to ramp routing is not possible:
: [[ImageFile:Jct_SPUI_off_outer_turnSPUI outer branch.pngPNG|500px]]
Where things get complicated is the inner branches leading to the single point. You need to avoid ramp-to-ramp in two directions and a reverse flow turn. '''Note:''' The ramp-to-ramp motion to facilitate a U-turn (the top left arrow in the image below) may or may not be allowed depending on the specific interchange. Please validate this turn.
: [[ImageFile:Jct_SPUI_off_inner_turnSPUI inner branch.pngPNG|700px]]
Luckily the entrance ramp restrictions are similar to the diamond interchange:
: [[ImageFile:Jct_SPUI_on_turnSPUI middle branch.pngPNG|400px]]
If you were to look at all the restricted turns at once, you may get the false impression that something is very wrong. But as you now know, a SPUI has almost as many restricted turns as allowed ones.
: [[ImageFile:Jct_SPUI_all_turnsSPUI disabled turns.pngPNG|300px]]
'''Note on Elevation: '''The two surface street segments (between the outer ramps and connected to the single point) and the four ramp segments connected to the single point should all be the same level, either one higher or one lower than the elevation of the freeway segments above/below the single point.
=== {{Anchor|Collector/Distributor Lanes}}Collector/distributor lanes ===
These are lanes parallel to, but physically separated from, the lanes of a Freeway that serve to keep merging traffic out of the flow of through traffic on the mainline freeway.
==== {{anchor|Collector/distributor interchanges}}Collector/distributor interchange ====
Some interchange configurations make use of collector/distributor lanes to separate lower-speed merging traffic from high-speed through traffic. This is often used in cloverleaf interchanges and in groups of nearby exits.
The [[Detour Prevention Mechanisms|detour prevention mechanism]] will discourage Waze from routing users onto the collector-distributor and back onto the freeway – as long as the city street name on the freeway is the same (or set to "no city") before, throughout, and after the collector-distributor. Previously this feature was not available and the ramps were set up to restrict the through route. Some of these ramp configurations may still be set up that way, so they can now be configured as pictured above with the through route enabled.
==== {{anchor|Complex collector/distributor interchanges}}Complex collector/distributor interchange ====
[[Image:Collector-distributor-exit.png|thumb|right|450px|Collector-distributor lanes used in an interchange on I-81 in Christiansburg, Virginia (Exits 118A-B-C)]]
=== {{Anchor| Diverging diamond interchange (DDI)|Diverging diamond interchange|Diverging_diamond_interchange|DDI}}Diverging diamond (DDI) ===
''See also:'' [[Wikipedia:Diverging_diamond_interchange|Diverging Diamond Interchange]] article on Wikipedia.